This article deals with synthesis of highly textured sodium cobaltate Na0.75CoO2 and changes of their properties at different ambient conditions. At the same time, we identified its peculiarities that influence the measured parameters to a degree that poses serious questions about this material’s potential for use. We have systematically studied the influence of humidity on the ceramic pellets and identified the conditions under which the material completely deteriorates. By performing microstructural and thermal analyses, coupled with a determination of the evolved gases, we identified the chemical reactions that are involved in this process. The changes in the physical parameters can be attributed to the reduction of cobalt and consequently to the formation of CoO inclusions, which increases the amount of sodium in the sodium cobaltate lattice.
COBISS.SI-ID: 27467815
In-situ-heating transmission electron microscopy (TEM) and X-ray diffraction (XRD) analyses were performed on the (Na(1−x)K(x)) 0.5Bi0.5TiO3 perovskite solid solution at the morphotropic phase boundary (MPB) in order to evaluate the structural contribution to the enhanced electromechanical properties of piezoelectrics. We found that after heating the lamellar domains do not reappear; instead, a tweedlike, nanodomain structure is established with the inphase tilt system to a large extent preserved. The XRD measurements of the MPB samples confirmed that the original structure of the MPB material is pseudocubic. These analyses reveal that the source of the enhanced electromechanical responses of piezomaterials at their MPBs is their “easily adaptable” relaxortype character with the field induced structural conformism.
COBISS.SI-ID: 26718503
The experimental conditions for the growth of shape controlled BaTiO3 particles in NaOH and Ba(NO3)2 aqueous and water/ethanol solutions using various TiO2 containing precursors were studied at 80°C–100°C. The different chemistries and physical characteristics of the precursors resulted in different BaTiO3 formation rates and morphologies. The electron microscopy observations supported a dissolution–precipitation mechanism as the primary reaction mechanism for the formation of BaTiO3 nanocrystals, which further aggregated into single crystalline star or square-like particles by oriented attachment. The modification in the water solution with ethanol is believed to influence both the nucleation and aggregation process and consequently influence the particle shape and size.
COBISS.SI-ID: 27166503
Recent density-functional theory calculations suggest that codoping TiO2 with donor–acceptor pairs is more effective than monodoping for improving photoelectrochemical water-splitting performance because codoping can reduce charge recombination, improve material quality, enhance light absorption and increase solubility limits of dopants. Here we report a novel ex-situ method to codope TiO2 with tungsten and carbon (W, C) by sequentially annealing W-precursor-coated TiO2nanowires in flame and carbon monoxide gas. The unique advantages of flame annealing are that the high temperature ()1000 °C) and fast heating rate of flame enable rapid diffusion of W into TiO2 without damaging the nanowire morphology and crystallinity. This is the first experimental demonstration that codoped TiO2:(W, C) nanowires outperform monodoped TiO2:W and TiO2:C and double the saturation photocurrent of undoped TiO2 for photoelectrochemical water splitting. Such significant performance enhancement originates from a greatly improved electrical conductivity and activity for oxygen-evolution reaction due to the synergistic effects of codoping.
COBISS.SI-ID: 26688551
In our study, pulsed laser deposition was used to prepare a SrTiO3 (STO) thin film on a H-terminated Si substrate. The main purpose of our work was to verify the ability of H-termination against the oxidation of Si during the PLD process and to analyze the resulting interfaces. In the first part of the study, the STO was deposited directly on the Si, leading to the formation of a preferentially textured STO film with a (100) orientation. In the second part, SrO was used as a buffer layer, which enabled the partial epitaxial growth of STO with STO (110)//Si(100) and STO[001]//Si[001]. The change in the growth direction induced by the application of a SrO buffer was governed by the formation of a SrO(111) intermediate layer and subsequently by the minimization of the lattice misfit between the STO and the SrO. Under the investigated conditions, approximately 10 nm thick interfacial layers formed due to reactions between the deposited material and the underlying Si. In the case of direct STO deposition, SiOx formed at the interface with the silicon, while in the case when SrO was used as a buffer, strontium silicate grew directly on the silicon, which improves the growth quality of the uppermost STO.
COBISS.SI-ID: 26882855